Editable planning geometry — not a code, compliance or safety determination.
Zone 0 ring area900 ft²
Intermediate ring area7,500 ft²
Extended ring area47,600 ft²
MethodRectangular offset geometry
A(d) = footprint enclosed at offset distance d
L = house length
W = house width
d = selected planning boundary
A(d) = (L + 2d)(W + 2d)
See how defensible-space geometry grows
The visualisation treats the house as a rectangle and expands that rectangle outward by each selected distance. The area of each ring is calculated from the difference between successive offset footprints.
This makes it easy to compare how a change in house size or planning distance affects the amount of surrounding land included in each zone.
The default example
For a 50 × 30 ft rectangular house with editable boundaries at 5 ft, 30 ft and 100 ft, the outer footprint is 250 × 230 ft. Subtracting the 1,500 ft² house footprint leaves 56,000 ft² of surrounding planning area.
Important limitation
Important: this is a geometry and planning calculator, not a wildfire-safety determination. Defensible-space rules, terminology and required distances differ by jurisdiction and site conditions. Real properties may also require non-rectangular geometry, slope, vegetation, access, structures, property boundaries and local regulations to be considered.